Seal assembly

ABSTRACT

A seal assembly for sealing a shaft configured to rotate in a main direction, the seal assembly including a stiffener and at least one elastomer seal member connected to the stiffener, the elastomer seal member including a seal region having a seal section configured to seal against a shaft and seal a to-be-sealed space, the seal section including a first screw thread web structure configured to pump a leakage fluid toward the to-be-sealed space when the shaft rotates in the main direction, a second annular, circumferentially extending web structure configured to sealingly abut on the shaft at least when the shaft is not rotating, and a third annular, circumferentially extending web structure configured to sealingly abut on the shaft at least when the shaft is not rotating, wherein the second web structure is axially spaced from the third web structure.

CROSS-REFERENCE

This application claims priority to German patent application no. 102016 220 179.4 filed on Oct. 17, 2016, the contents of which are fullyincorporated herein by reference.

TECHNOLOGICAL FIELD

The disclosure is directed to a seal assembly for sealing a rotatableshaft.

BACKGROUND

In particular in internal combustion engines and transmissions in theautomotive sector, particular requirements with respect to service life,low friction, and installation safety are placed on seal rings usedthere. A main direction of rotation is often present in suchapplications, i.e., the to-be-sealed shaft rotates predominantly in thismain direction of rotation. A rotating in the opposite direction(so-called “reverse travel”) then only occurs in a very short timeperiod. In this regard in the development to date of seal elements forthese applications a focus has been placed on the achieving of a highand reliable tightness with rotating in the main direction of rotationand with stationary shaft, while the tightness with reverse travel wasoften secondary.

For example, radial shaft seal rings are known includingpolytetrafluoroethylene (PTFE) and a spiral pumping structure, forexample, for a synthetic oil of the internal combustion engine. Thesliding properties of PTFE-based shaft seals can be improved byadditives such as graphite or molybdenum sulfide. However, PTFE here isrelatively inelastic, with the result that disadvantages arise withrespect to the static tightness of corresponding shaft seals. It is thusknown to close an existing seal gap with waxes or greases for pressure-and/or vacuum-tests of such shaft seals. These volatilize in operationof the seal.

Improved seal assemblies have already been proposed that reduce suchproblems. Thus from DE 10 2007 036 625 A1 (a family member of US2010/0237567) a seal element is proposed for sealing a shaft intendedfor rotating in a passage opening of a housing for the shaft, which sealelement includes a stiffening part and an elastomer element connectedthereto. The elastomer part comprises a first seal region for a staticsealing abutment on the housing part, as well as a second seal regionincluding a seal section configured and provided for sealing abutment onthe shaft. The seal section includes a screw thread-type return pumpingstructure and a ring-type region, in the form of a closed line, lying onthe free axial end. Due to the use of an elastomer the seal assembly hasan increased elasticity, with the result that a pressure- and/orvacuum-testing is possible without applying additional materials ontothe seal section. With the shaft rotating in the main direction,escaping leakage fluid is pumped by the return pumping structure towardthe to-be-sealed space. In contrast, with a stationary shaft thering-type region acts as a static seal.

Numerous proposed seal assemblies have the problem that a leakageresults with a reversing of the shaft rotation direction. Solutions havealso already been proposed for this problem. Thus in DE 10 2004 020 966A1 (a family member of US 2005/0242521) a radial shaft seal is disclosedthat is formed from an elastomeric material and includes a surfacesection that is provided with hydrodynamically acting return-pumpinggrooves for leakage liquid. These return-pumping grooves extend on theaxial free end of the surface section in a seal bead. The return-pumpinggrooves are formed by inwardly directed cutting tips. For sufficientsealing the seal bead has a minimum contact width of 0.1 mm with theshaft. With the proposed seal assembly the contact width should be atmost 0.8 mm, since otherwise a sufficient lubricating cannot be ensured.Due to this comparatively large contact width wear is increased.

SUMMARY

It is an aspect of the present disclosure to provide an improved sealassembly that has optimized dynamic and static seal properties and inaddition is available to a wide range of applications with low wear andis manufacturable with little effort.

According to one advantageous embodiment of the disclosure a sealassembly is provided for sealing a shaft provided for rotating,comprising the following features:

-   -   a stiffening part and at least one elastomer part connected to        the stiffening part,    -   the elastomer part includes a seal region including a seal        section configured for sealing a to-be-sealed space,    -   the seal section includes a first screw thread-type web        structure, using which a leakage fluid is pumpable back into the        to-be-sealed space,    -   the seal section includes a second web structure, extending in        the circumferential direction and closed, (for example, an        annular rib) that is provided for sealing abutment on the shaft        at least with a not-rotating shaft,    -   the seal section includes a third web structure extending in the        circumferential direction and closed, (for example, an annular        rib) that is provided for sealing abutment on the shaft at least        with a non-rotating shaft, and    -   the second web structure is disposed axially between the first        and the third web structure and spaced axially from the third        web structure.

With a rotating shaft, escaping leakage fluid can be pumped back in theto-be-sealed space by the first screw thread-type web structure. This isadvantageous in particular with dynamic loading of the seal inapplications wherein a main direction of rotation is present, since inthis case leakage fluid is reliably pumped back even underneath thesecond and third web structure by a built-up pumping pressure.

Due to the second and third web structures, extending in thecircumferential direction and closed, and in particular their axialspacing, both a static sealing with stationary shaft and a sufficientdynamic sealing in the case of a shaft temporarily rotating against themain direction of rotation are possible. The thus cascadingly disposed,respectively closed web structures sufficiently hold back escapingleakage fluid independent of the direction of rotation. In the staticcase, i.e., with stationary shaft, both web structures sealingly abut onthe shaft with the result that in this case no leakage fluid can escape.Due to the providing of two such web structures with axial spacing, evenwith a leakage of one of the web structures a temporary reliable sealingis ensured by the other encircling web structure. Due to the axialspacing of the second and third web structure a reservoir can formbetween them, wherein small amounts of leakage fluid can collect.

In known seals a single seal bead is already known as a static seal witha stationary shaft, to which a return-pumping structure connects, oftenembodied as a single- or multi-start spiral of a single direction ofrotation. In the dynamic case with rotating of the shaft against themain direction, such an assembly cannot ensure a reliable sealing. Suchreturn-pumping structures only have the desired pumping effect towardthe to-be-sealed space with rotating of the shaft in the main direction.With rotating against the main direction (the so-called “reversetravel”), however, such a structure unavoidably has an undesired pumpingeffect toward the environment. Escaping leakage fluid is thus pumpedtoward the environment. In the dynamic case of the rotating shaft it isnecessary that the seal bead is lubricated by a thin oil film. Otherwiseheavy wear of the seal would occur due to the increased friction. Thepumping structure connecting to the seal bead then has the effect ofactively pumping oil standing below the seal bead actively away from ittoward the environment. The leakage is thereby even actively increased.The disclosure avoids this disadvantage by providing the axially spacedthird web structure, which is in direct operative connection with thefirst, screw thread-type web structure. In contrast, the second webstructure directly axially abuts on the first web structure. It is thusin operative connection with the first web structure.

In the case of the shaft rotating against the main direction thecascadingly disposed second and third web structure sufficiently delay aleakage, since escaping leakage fluid initially collects in thereservoir. The reservoir can be dimensioned according to the applicationsuch that with typical time durations of a return travel and an assumedleakage it does not completely fill, with the result that no leakagefluid can pass under the second web structure and thus into theenvironment. With the rotating in the main direction inevitablyfollowing after the reverse travel, escaped leakage fluid is activelypumped by the first web structure back underneath the second webstructure into the reservoir and pumped with the leakage fluid collectedthere back under the third web structure into the to-be-sealed space. Aleakage is thus reliably prevented.

In one advantageous embodiment of the disclosure the seal section isformed in the region of a free axial end such that in the installedstate of the seal assembly the third web structure is pressed onto theshaft with a first radial force (the so-called “contact pressure”),which is smaller than a second radial force with which the second webstructure is pressed onto the shaft. Preferably the first radial forceis between 40% and 70% smaller than the second radial force. Due to theelastic material chosen the radial forces with which the web structuresare pressed onto the shaft are typically subject to fluctuations thatarise due to the distribution of a radial force acting on the first webstructure. Thus a total radial force exerted overall by the elasticityof the material on all web structures is distributed somewhatdifferently on the different web structures at different angularpositions along the circumference in the respective axial extensionalong the shaft, since the screw thread-type first web structure hascontact with the shaft at every angular position at different axialpositions. It is relevant that the first radial force is smaller alongthe entire circumference than the second radial force. This has thepositive effect that the leakage fluid can be more easily pumped backunder the third web structure into the to-be-sealed space than it canpass through the second web structure toward the environment.

In one advantageous design of the disclosure the seal section in theregion of the first web structure is configured such that the first webstructure is pressed onto the shaft along its extension with varyingradial force distribution, wherein a maximum of the radial force occursat a position of the first web structure that is axially spaced from thesecond web structure. The radial force preferably initially increasestoward the second web structure, with the result that each winding ofthe web structure is pressed onto the shaft with a higher radial forcethan the previous one. After exceeding a maximum radial force in anaxial spacing to the second web structure the radial force decreasesagain. This causes an optimized pumping effect of the first webstructure.

In one advantageous design of the disclosure a groove-type recessextending in the seal section in the circumferential direction islocated between the second and third web. This recess serves as adefined reservoir for leakage fluid passing through the third webstructure in the static or dynamic case, in particular with the shaftrotating backwards. The dimensioning of the recess can be adapted in asimple manner according to the intended application.

In one advantageous design of the disclosure, in the not-installed stateof the seal assembly the inner diameter of the first web structurecontinuously decreases toward one free axial end, the inner diameter ofthe second web structure is smaller than the smallest inner diameter ofthe first web structure, and the inner diameter of the third webstructure is smaller than the inner diameter of the second webstructure. The decrease of the inner diameter toward the free axial endis preferably linear. The decrease of the inner diameter preferablyoccurs by a factor in the range between 0.5 and 1.0, particularlypreferably of 0.8. That is, for example, with an axial viewing distanceof two inner diameters of 1 mm, the inner diameters differ by 0.8 mm,i.e., decrease by 0.8 mm per millimeter of axial offset. Thiscorresponds to an opening angle of a cone of approximately 45° or of22.5° with respect to the main axis of the seal assembly. With thisdecrease, in the installed state a preferred pressure distributionarises with web structures abutting on the shaft, which leads to lowwear with simultaneously high tightness.

In one advantageous design of the disclosure, in the installed state ofthe seal assembly the inner diameters of the web structures decreaselinearly toward one free axial end of the seal section. The surfaces ofthe web structures lie on a cone tapering toward the free axial end.With installed seal assembly a defined course of the radial forces canthereby be achieved and thus an optimizing of the seal effect.

In one advantageous design of the disclosure the axial spacing of thesecond and third web structure falls between 40% and 60% of the pitch ofthe screw thread of the first web structure. The spacing preferablyfalls at 50%. For example, the axial spacing is 0.35 mm with a screwthread pitch of 0.7 mm. This results in an optimal size of the reservoirthus formed for leakage fluid in conjunction with the return-pumpingeffect of the first web structure.

In one advantageous design of the disclosure the third web structure isassociated with a free axial end of the seal section. The axial free endis the end of the sealing section that lies toward the to-be-sealedspace. A connecting point of the elastomer part lies axially opposed tothe stiffening part. The screw thread depth of the first web structurepreferably decreases in the extension toward the second web structureand is configured merging into the second web structure. Due to thisassembly, in particular in the dynamic case of the rotating of the shaftin the main direction the hydrodynamic return pumping of leakage fluidcan be optimized. The decreasing screw thread depth and the transitioninto the second web structure generates an increasing pressure in thescrew thread toward the second web structure, which pressure issufficiently large to pump leakage fluid back under the second webstructure into the reservoir. If the reservoir between the second andthird web structure is filled with leakage fluid, and if further leakagefluid is pumped back by the first web structure, then leakage fluid isalso pumped under the third web structure back into the to-be-sealedspace.

In one advantageous design of the disclosure the web structures areformed on the seal section from webs disposed there, wherein the webshave similar cross-sections. Such a seal assembly is particularlycost-effective and manufacturable with higher precision, which isdescribed further below. Thus the relevant surface structure of avulcanizing tool can preferably be manufactured in a single operationusing a single cutting plate, with the result that the structures can begenerated as accurately as possible. A setting down or even a changingof the cutting plate is not required. Seal assemblies manufactured usingthis cutting tool are consequently also very accurately manufactured,with the result that increased leakages due to imprecisions inmanufacturing are precluded.

In one advantageous design of the disclosure the cross-section of thewebs is configured triangular, wherein the triangular profile has such ashape that an asymmetric pressure distribution is present in the sealingcontact to the shaft such that even with rotating of the shaft againstthe main direction a pumping effect is achievable. Due to the asymmetricdesign of the cross-section of the webs, even with the shaft rotatingagainst the main direction, wherein the screw thread-type first webstructure achieves no pumping effect or an undesired pumping effect asdescribed above, the second and third web structure already achieve areturn-pumping effect, with the result that leakage fluid is pumped backinto the to-be-sealed space. Since the time duration of the backwardrotating shaft is usually significantly smaller, this pumping effect ofthe second and third web structure can be typically be significantlylesser than that of the first web structure with the shaft rotating inthe main rotational direction.

In one advantageous design of the disclosure a first leg of thetriangular cross-section, which lies on the side of the free axial endof the seal section, is configured with a smaller inclination withrespect to the shaft main axis than the second, axially opposing leg.Such a symmetrically configured triangular shape reliably ensures asufficiently asymmetric pressure distribution in the seal contact to theshaft, with the result that the pumping effect just described isachieved in a simple manner.

The first leg preferably encloses an angle α with the shaft main axis orthe surface thereof that falls between 40° and 90°. The second legencloses an angle β with the shaft main axis or the shaft surface thatfalls between 5° and 35°. Here α preferably falls between 55° and 80°,still more preferably at 75°. In contrast, β optimally falls between 15°and 20°, still more preferably at 15°. With such embodiments of theangle the asymmetric pressure distribution is greatest with respect toits pumping effect.

In one advantageous design of the disclosure the triangularcross-section has a rounded shape at the tip with which the websealingly abuts on the shaft. This preferably has a radius between 0.03and 0.1 mm, particularly preferably of 0.05 mm With a typical localradial force on the web structures in the range of 0.4 to 3 N an optimalcontact pressure thereby arises of the web onto the shaft with a verylow contact area. Thus with such a seal assembly the friction can besignificantly reduced compared to known seal assemblies, wherein due tothe configuration of the three corresponding web structures the sealbehavior is also optimized by the distribution of the total radialforce.

Further advantages, features, and details of the disclosure arise fromthe exemplary embodiments of the invention described below withreference to the Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section through an upper half of anembodiment of the disclosure,

FIG. 2 shows a sectional enlargement of the seal section of theembodiment according to FIG. 1 in the installed state,

FIG. 3 shows a sectional enlargement of the axial end of the sealsection,

FIG. 4 shows a sectional enlargement of the seal section of theembodiment according to FIG. 1 in the not-installed state,

FIG. 5 shows a section of a mold part for manufacturing an embodiment ofthe disclosure, and

FIG. 6 schematically shows a part of the manufacturing process of avulcanizing tool for the embodiment of the disclosure.

DETAILED DESCRIPTION

FIG. 1 shows, as an exemplary embodiment of the disclosure, alongitudinal section through an upper half of a seal element 1 in afirst embodiment. The depiction shows the seal element 1 in theinstalled state, wherein a housing and a shaft are not shown for betterclarity. The ring-shaped seal element 1 comprises a first stiffeningpart (stiffener) 3, which is typically manufactured from a metallicplate. The seal element 1 further comprises an elastomer part 5connected to the stiffening part 3. The elastomer part 5 is formed froman elastomer material, in particular a fluoroelastomer, and connected tothe stiffening part 3 by a vulcanizing.

Here the elastomer part 5 comprises a seal region 9 whose outer surfaceis configured for statically sealing abutment on the not-depictedhousing part in the region of a passage opening for the to-be-sealed,not-depicted shaft. Here, for example, it is the housing of an internalcombustion engine, wherein a to-be-sealed oil space M of the motor isdisposed on the left side of FIG. 1 and an air side U, for example,associated with the surrounding atmosphere, is located on the right sideof FIG. 1.

The elastomer part 5 further comprises a second seal region 11 that withintended installation of the seal element 1, as depicted in FIG. 1,comprises an essentially hollow-cylindrical seal section 13 abutting onthe shaft. This then merges toward the right side into a section 15expanding in a trumpet-shaped manner. In the embodiment depicted thetrumpet-shaped section 15 thus protrudes into the oil space M with itscross-section decreasing into the oil space M. Finally the elastomerpart 5 includes a second seal lip 17 toward the air side U. This has nocontact to the shaft and keeps coarse contaminants away from the sealregion 11.

Here at least the inner surface of the hollow-cylindrical seal section13 is formed with the screw thread-type return-pumping structure, whichwith a rotating of the shaft with the intended main rotational directionexerts a reverse-pumping effect on oil penetrating between the shaft andthe seal section 13.

On the left end of the seal section 13 in the depiction in FIG. 1, i.e.,on the free axial end, the screw thread of the return-pumping structureends at a circular-ring-type, radially encircling, closed region 21,including a circular-cylinder-casing-type inner wall, of the sealsection 13, whose design will be explained in detail with reference toFIGS. 2 and 3.

A sectional enlargement of the seal region 13 of the embodiment of FIG.1 is depicted in FIG. 2. Here for illustration of significant aspects ofthe disclosure the contact of the seal region with the shaft (notdepicted) is indicated by a line 101 without covering the essentialstructure of the seal region 13. The seal region 13 includes a first webstructure that is embodied as a screw thread-type return-pumpingstructure 103. The seal region 13 furthermore includes a second webstructure and a third web structure that are each embodied in closedwebs 105 and 107 extending in the circumferential direction. The webs105 and 107 are disposed axially spaced, wherein the web 107 isassociated with the axial end of the sealing region 13, while the web105 is disposed on the end of the return-pumping structure. Consequentlythe web 105 lies between the return-pumping structure 103 and the web107.

At least with a non-rotating shaft the webs 105 and 107 are provided forsealing abutment on the shaft. Here in conjunction with the materialproperties of the elastomer they form the prerequisite that even with anon-rotating shaft the seal element abuts on the shaft in a gas- andfluid-tight manner, with the result that, for example, for monitoring ofthe correct installation of the seal element and the seal effect of theinternal combustion engine in the context of the assembly process apressure- and/or vacuum testing can be undertaken without furthermaterials having to be applied between the seal section 13 and theshaft.

The screw thread of the return-pumping structure 103 merges into the web105 such that the width and depth of a groove 104 defined by thereturn-pumping structure 103 decrease with a profile remaining equallyproportioned. This has the positive effect that with relatively simplemanufacturability the return-pumping effect is positively influenced tothe effect that with a rotating shaft a pressure increase is generatedin the leakage fluid to be pumped back, with the result that leakagefluid is reliably pumped back underneath the web 105. The detaileddesign and the interaction of the webs 105 and 107 are explained indetail with reference to FIG. 3.

The region A of the embodiment of the seal assembly of FIG. 2 isdepicted enlarged in FIG. 3. Here in particular the two self-enclosedwebs 105 and 107 can be seen in detail. Between the two axially spacedwebs 105 and 107 a recess 131 is formed that forms a reservoir forescaping or pumped-back leakage fluid. The webs 105 and 107 have aspacing a whose size is between 40% and 60% of the screw thread pitch ofthe return-pumping structure 103. Here an optimal volume of thereservoir arises with respect to the selected pumping capacity of thereturn-pumping structure 103.

The webs 105 and 107, as well as the return-pumping structure 103, havea similar cross-section geometry, wherein this is configured triangularand respectively includes two legs 133 and 135 and a rounded tip lyingbetween them, which is illustrated in an exemplary manner with referenceto the web 107. With the rounded tip 137 the seal respectively abuts onthe surface of the shaft, which here in turn is indicated by the line101. The radius of the tip 137 preferably falls between 0.03 and 0.10mm, whereby a very small contact surface arises with the surface of theshaft and thus a lowest possible friction between the seal and theshaft. Ideally the radius of the rounded tip falls at 0.05 mm. Herethere is an optimal ratio between contact width of the seal with theshaft and the prevailing friction or seal effect. Due to the flexibilityor stiffness of the elastomer part 5, in one exemplary design of theseal a predominant total radial force results of approximately 5 N alongan axial line lying on the shaft, such as, for example, the line 101.This total radial force is distributed on the surface tips of the webs105 and 107, which surface tips are along the line in contact with theshaft, as well as the return-pumping structure 103, which typicallyleads to local radial forces in the range of 0.4 to 3 N, which act onthe rounded tip. These local radial forces lead only to a very slightflattening of the seal cross-section due to pressure on the shaft, withthe result that in operation the contact width is optimized andcomparatively small.

With the webs 105 and 107 and the return-pumping structure 103, the leg135 pointing toward the environment encloses an angle β with the surfaceor the main axis of rotation of the shaft. The angle β preferably fallsbetween 5° and 35°. Particularly preferably β falls between 15° and 20°.In typical application cases in the automotive field β optimally fallsat 15°. The optimum angle β here can by all means vary between differentapplications. The opposite leg 133 of the triangular cross-sectionstructure encloses an angle α with the surface or axis of rotation ofthe shaft that is preferably between 40° and 90°. Particularlypreferably the angle α falls between 55° and 80°. In a typicalapplication with the webs 105 and 107 α optimally falls at 75°, it isthus equal for all. Alternatively as in the exemplary embodiment of thedisclosure shown in FIG. 3 α can fall at 45° only with web 107; howeverwith 105 and with the return-pumping structure 103 at barely 80°. By theselection of different sized angles α and β, with the abutting of theweb on the shaft an asymmetric pressure distribution on the contactsurface is generated which leads to an active return pumping of leakagefluid. This is relevant in particular if with a shaft rotating againstthe main direction of rotation a tendency arises in the fluid to passunderneath the web 107. In the case of the shaft rotating against themain direction of rotation the return-pumping structure 103 has noreturn-pumping effect. Rather, in this case the return-pumping structure103 even pumps the fluid actively toward the environment U. Therefore itmust be ensured by the webs 105 and 107 alone that no leakage fluid canreach the environment U. Here most of the leakage fluid is alreadyretained or actively pumped back into oil space M by the optimization ofthe web 107. Although with the shaft rotating against the main directionof rotation the pumping capacity of the entire seal section 13 issignificantly reduced, compared to the other case of the shaft rotatingin the main direction of rotation, by the elimination of the effect ofthe return-pumping structure 103, the significantly lower amount ofleakage fluid then due in particular to the significantly shorter timeduration of the rotation and the lower rotational speeds is in this casenonetheless sufficient.

The leakage fluid nevertheless escapes under certain circumstances dueto the very small and thereby friction-optimized contact width of theweb 107 with the shaft and collects in the recess 131 between the webs105 and 107. There it is pumped back in turn by the optimized geometryof the web 105 toward the web 107 and thus toward the oil space M. Thewebs 105 and 107 cascadingly disposed in this manner thus ensure in animproved manner that even with the shaft temporarily rotating againstthe main direction no leakage fluid can reach the environment U. Here atthe same time a small contact width of the webs 105 and 107 with theshaft and thus a friction-optimized seal is given. Known seals includingonly one web are for this purpose only insufficient or sufficient due toan increased friction, for example as a consequence of a larger contactsurface in the position.

A similar embodiment to those in FIGS. 1 to 3 is sectionally depicted inFIG. 4; however here in the not-installed state. In contrast to thedepiction of the installed state in FIGS. 1 to 3, here the geometry ofthe elastomer part 5 can be seen in particular in the region of the sealregion 11. This tapers in a cone-shaped manner toward the free axialend, which is illustrated by the line 301. Accordingly the surfaces ofthe webs 105 and 107, as well as the return-pumping structure 103, lieon the surface of a corresponding cone. The inner diameter of thereturn-pumping structure 103 consequently decreases linearly in theaxial direction. The inner diameter of the web 105 is correspondinglyeven smaller, while the inner diameter of the web 107 is smallest.

The line 303 indicates the surface of a not-depicted shaft on which thewebs 105 and 107, as well as partially the return-pumping structure 103,abut in the installed state. It is clear that an increasing widening ofthe elastomer part 5 along the axial extension of the seal region 11results from the installation of the seal assembly. Due to theelasticity of the elastomer part 5 this results in a total radial forceby which the webs 105 and 107 and the return-pumping structure 103 arepressed onto the shaft. A local radial force (“contact pressure”)respectively acts on the webs 105 and 107 and the return-pumpingstructure 103; the size varies due to the geometry of the webs 105 and107 and of the return-pumping structure. The webs 105 and 107 lieaxially at the same position along each imaginary axially extending lineon the shaft, such as, for example, the line 103. In contrast, due tothe screw thread-type structure the axial position of the webs of thepumping structure 103 is different with each angular position of theline along the circumference of the shaft. Thus with different angularpositions a different distribution of the total radial force arises onthe different webs. The local radial force has a maximum in the axialextension that, with each angular position, lies in the region of thereturn-pumping structure. Accordingly the local radial force acting onthe web 105 is lower than this maximum. The local radial force acting onthe web 107 is in turn lower than the maximum and than the local radialforce acting on the web 105. In direct comparison the web 107 is pressedless onto the shaft than the web 105, and this in turn less than the tipof the return-pumping structure 103 that is pressed onto the shaft withmaximum force. This combination of local radial forces is optimized withrespect to the pumping behavior with the shaft rotating in the maindirection, the pumping behavior with the shaft rotating against the maindirection, and the wear.

The described seal assembly additionally has the advantage that it ismanufacturable in a particularly simple manner Usually the elastomerpart 5 used is produced by injection molding using a tool that has theshape as a cavity of the seal assembly to be produced. In a known mannerelastomer is introduced in the cavity and vulcanized. The manufacturingof the tool is very complex and associated with high costs. Here, forexample, metal parts are machined and brought into the desired shape,which assembled form the cavity. For this purpose the required structureof the webs or recess in one of the metal parts are manufactured using aplurality of cutting tools. The cutting plates have different geometriesin order to be able to manufacture the often-different geometries of thewebs. The cutting plates are subsequently advanced to the metal partwhile it is rotating so that a machining results. Due to the smalldimensions of the webs, with each change of the cutting tool highrequirements are placed on the precision of the new position of thecutting tool. Generally this results in deviations from the desiredgeometry. The inaccuracies thus resulting transfer to the manufacturedseal assembly, which can impair its reliability in operation.

In the preferred embodiment of the disclosure the cross-sectionalgeometry of the spiral return-pumping structure 103 as well as that ofthe two encircling webs 105 and 107 are designed such that thecorresponding shaped part of the tool can be produced using only asingle cutting plate in a single continuous manufacturing process. Asetting down of the cutting tool for changing thereof is not required.Both the exact shape and position of the return-pumping structure 103and the two webs 105 and 107 with respect to each other is therebyensured, since in contrast to the manufacturing of known vulcanizingtools the cutting plate need not be changed, whereby the manufacturingprocess is not interrupted. In addition, due to the essentiallyidentical geometry all webs can be manufactured using the same cuttingplate. Thus in particular due to the very small radii of the roundedtips an optimal pressure distribution is also ensured and even thesmallest error in the manufacture of the vulcanizing tool and thus ofthe elastomer is precluded.

In FIG. 5 a section of a shaped part 401 is schematically depicted.Using the shaped part 401, seal assemblies according to the disclosurecan be manufactured with known methods. For example, such seals aremanufactured by vulcanizing in the injection molding method. Externallyand radially encircling, the shaped part 401 has the inverse structureof the seal region 11 of the elastomer part 5 of the seal assembly 1according to FIGS. 1 to 4. The structure accordingly comprises a spiralgroove 403 tapering axially leftward having a defined contour by whichthe return-pumping structure 103 is formed by filling with elastomerduring the vulcanizing process. In this respect the geometry of thegroove 403 corresponds exactly to the geometry of the web of thereturn-pumping structure 103. The groove 403 ends in a region 404 in agroove 405 extending in the circumferential direction, whose geometry inturn corresponds to the geometry of the web 105. Axially spaced there isa further groove 407 extending in the circumferential direction whosegeometry in turn corresponds to the geometry of the web 107. Anelevation 406 lying therebetween has the geometry of the recess 131.

The shaped part 401 tapers in a cone-shaped manner in the axialdirection, which is illustrated by the line 408. In particular thedeepest points of the grooves 403, 405, and 407 lie on the outer surfaceof a corresponding cone. Accordingly the grooves 403, 405, and 407 havedifferent inner diameters with respect to the circumferential direction,wherein due to the spiral course the inner diameter of the groove 403continuously decreases and the groove 407 has the smallest diameter. Inthe not-installed state a seal assembly thereby manufactured also tapersin a cone-shaped manner toward the free axial end. In an analogousmanner the inner diameters of the webs 105 decrease, as well as theradius of the return-pumping structure 103. In contrast, in theinstalled state of the seal assembly the webs 105 and 107 arising fromthe grooves, as well as the return-pumping structure 103, are widened bythe shaft, which due to the elasticity of the elastomer leads to aradial force. The webs 105 and 107 are sealingly pressed by this ontothe shaft. In typical applications the return-pumping structure 103abuts only partially on the shaft, for example, on the first threewindings starting with web 105.

In FIG. 6 the manufacturing process of the shaped part 401 isschematically depicted. For this purpose a cutting plate 501 is used forcutting ablation of material in a basically known manner in order togenerate the grooves 403, 405, and 407. To illustrate the process thecutting plate 501 is depicted superimposed in a plurality of processphases that in reality temporally follow one another. In themanufacturing process only one cutting plate 501 is used that isoperated, for example, under CNC control, while the not-yet completedshaped part 401 rotates about its central axis. In addition, for betterillustration the cutting plate 501 is depicted slightly spaced from theshaped part 401. In the actual process both parts are in operativecontact.

To manufacture the spiral groove 403 the cutting plate 501 is initiallycontinuously moved axially toward the free end and to a lesser degreeradially inward (thus in the depiction of FIG. 5 toward lower leftparallel to line 408), which is illustrated by the arrow 511. Here theshaped part rotates, with the result that the groove 403 continuouslyarises. At point 513 the cutting plate 501 is held for a defined time,namely that required for one revolution, in order to generate theencircling groove 405. Subsequently the cutting plate 501 is movedradially outward, which is indicated by the arrow 515. Thereafter thecutting plate 501 is moved axially leftward along the arrow 517 andmoved radially inward along the arrow 519 after an established distancethat then corresponds to the spacing of the webs 105 and 107 in the sealassembly. Subsequently it is moved axially leftward and radially outwardalong the arrow 521. The groove 407 is thereby generated.

In this manner a shaped part 401 can be produced with extremely precisegeometry in a single operation using a CNC-controlled milling machine,using which shaped part 401 seal assemblies can then in turn bemanufactured also with extremely exact geometry and thus high tightnessand reliability.

Representative, non-limiting examples of the present invention weredescribed above in detail with reference to the attached drawings. Thisdetailed description is merely intended to teach a person of skill inthe art further details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the invention.Furthermore, each of the additional features and teachings disclosedabove may be utilized separately or in conjunction with other featuresand teachings to provide improved seal assemblies.

Moreover, combinations of features and steps disclosed in the abovedetailed description may not be necessary to practice the invention inthe broadest sense, and are instead taught merely to particularlydescribe representative examples of the invention. Furthermore, variousfeatures of the above-described representative examples, as well as thevarious independent and dependent claims below, may be combined in waysthat are not specifically and explicitly enumerated in order to provideadditional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

REFERENCE NUMBER LIST

1 Seal element

3 Stiffening part

5 Elastomer part

9, 11 Seal region

13 Seal section

15 Section

17 Seal lip

21 Region

101 Line

103 Return-pumping structure

104 Groove

105, 107 Web

131 Recess

133, 135 Leg

137 Tip

106, 106′ Opening

301, 303 Line

401 Injection molding

403, 405, 407 Groove

406 Elevation

408 Line

501 Cutting plate

511, 515, 517, 519, 521 Arrow

513 Point

What is claimed is:
 1. A seal assembly for sealing a shaft configured torotate in a main direction, the seal assembly comprising: a stiffenerhaving first and second ends and at least one elastomer seal memberconnected to the stiffener, the second end being located radiallyinwardly relative to the first end, the elastomer seal member includinga seal region having a seal section configured to seal against a shaftand seal a to-be-sealed space relative to an environment, the sealsection having an axial free end positioned axially farthest from thesecond end of the stiffener, the elastomer seal member further forming atrumpet section located between the seal section and the stiffener, theseal section including a screw thread-type return-pumping structureconfigured to pump a leakage fluid toward the to-be-sealed space whenthe shaft rotates in the main direction, a second annular, self-enclosedring web structure configured to sealingly abut on the shaft at leastwhen the shaft is not rotating, and a third annular, self-enclosed ringweb structure configured to sealingly abut on the shaft at least whenthe shaft is not rotating, wherein the screw thread-type return-pumpingstructure flows into the second annular, self-enclosed ring webstructure, the third annular, self-enclosed ring web structure islocated closer to the axial free end of the seal section than the secondannular, self-enclosed ring web structure, the second annular,self-enclosed ring web structure is axially spaced from the thirdannular, self enclosed ring web structure with a recess formedtherebetween, the seal structure being configured such that greaterpressure is required for fluid to pass from the screw thread-type returnpumping structure past the second and third annular, self-enclosed ringstructures into the to-be-sealed space than is required for fluid topass from the to-be-sealed space past the second and third annular,self-enclosed ring structures into the screw thread-type return pumpingstructure to reduce leakage from the to-be-sealed space when the shaftchanges from rotating in the main direction to rotating in an oppositedirection.
 2. The seal assembly according to claim 1, including anannular groove between the second annular, self-enclosed ring webstructure and the third annular, self-enclosed ring web structure. 3.The seal assembly according to claim 1, wherein, before being installedon the shaft, the inner diameter of the screw thread-type return-pumpingstructure decreases linearly toward the free axial end of the sealsection.
 4. The seal assembly according to claim 1, wherein the thirdannular, self-enclosed ring web structure is located between the secondannular, self-enclosed ring web structure and the free axial end of theseal section.
 5. The seal assembly according to claim 4, wherein thescrew thread-type return-pumping structure merges smoothly into thesecond annular, self-enclosed ring web structure.
 6. The seal assemblyaccording to claim 1, wherein the second annular, self-enclosed ring webstructure is disposed between the screw thread-type return-pumpingstructure and the third annular, self-enclosed ring web structure. 7.The seal assembly according to claim 1, wherein an axial spacing fromthe second annular, self-enclosed ring web structure to the thirdannular, self-enclosed ring web structure is 40-60% of a pitch of thescrew thread of the screw thread-type return-pumping structure.
 8. Theseal assembly according to claim 7, wherein the first flank faces thefree axial end of the seal section and the second flank faces away fromthe free axial end and wherein the first angle is greater than thesecond angle.
 9. The seal assembly according to claim 8, wherein thefirst angle is between 40° and 90°, and the second angle is between 5°and 35°.
 10. The seal assembly according to claim 1, wherein the screwthread of the screw thread-type return-pumping structure has asubstantially constant, generally triangular, cross section, the screwthread having a first flank making a first angle with the shaft and asecond flank making a second angle with the shaft, the second anglebeing different than the first angle.
 11. The seal assembly according toclaim 10, wherein the first flank meets the second flank at a roundedtip portion of the screw thread-type return-pumping structure.
 12. Theseal assembly according to claim 1, including an annular groove betweenthe second annular, self-enclosed ring web structure and the thirdannular, self-enclosed ring web structure, wherein, before beinginstalled on the shaft, the inner diameter of the screw thread-typereturn-pumping structure decreases linearly toward the free axial end ofthe seal section, wherein the third annular, self-enclosed ring webstructure is located between the second annular, self-enclosed ring webstructure and the free axial end of the seal section, wherein the screwthread-type return-pumping structure merges smoothly into the secondannular, self-enclosed ring web structure, wherein the second annular,self-enclosed ring web structure is disposed between the screwthread-type return-pumping structure and the third annular,self-enclosed ring web structure, and wherein an axial spacing from thesecond annular, self-enclosed ring web structure to the third annular,self-enclosed ring web structure is 40-60% of a pitch of the screwthread of the screw thread-type return-pumping structure.
 13. The sealassembly according to claim 12, wherein the screw thread of the screwthread-type return-pumping structure has a substantially constant,generally triangular, cross section, and has a first flank facing thefree axial end of the seal section making an angle between 40° and 90°with the shaft and a second flank facing away from the free axial end ofthe seal section and making an angle of between 5° and 35° with theshaft, and wherein the first flank meets the second flank at a roundedregion.
 14. The seal assembly according to claim 1, wherein the secondannular, self-enclosed ring web structure comprises a continuous annularrib.
 15. The seal assembly according to claim 14, wherein the thirdannular, self-enclosed ring web structure comprises a continuous annularrib axially spaced from the second annular, self-enclosed ring webstructure.